Following a chemical attack on British soil connected to the Kremlin, British Prime Minister Theresa May expelled 23 Russian diplomats from the United Kingdom: The firmest rebuke of Russian President Vladimir Putin in the Trump era.

By severing diplomatic ties and imposing new sanctions against Moscow, May established a new precedent for Western powers in dealing with a regime that flagrantly tests rules put forth by the international community.

“They’re trying to convey that it’s not acceptable to carry out extrajudicial killings that also endanger British citizens on British soil. This has been a long time coming, frankly,” Hal Brands, the Henry Kissinger Distinguished professor at Johns Hopkins University, told Observer. “There’s been a long history of Russia poisoning or otherwise targeting dissidents and exiles in the United Kingdom.”

Because the chemical attacks in Britain incapacitated the target’s daughter and others exposed, it was “very difficult” for the May government to avoid sending a message. Though Brands questioned whether Britain’s sanctions will be a sufficient response to punish Russia for assassinations executed on foreign soil, he noted their implementation alone seeks to preserve the legitimacy of the liberal international order.

“There’s a perception in the United Kingdom, but also the United States, that authoritarian countries like Russia, China and Iran are increasingly testing the rules and the contours of the international order and that it is unlikely they will stop doing so until they meet some form of resistance,” explained the professor. “A more competitive and hard-nosed approach is going to be necessary to defend that order.”

The liberal international order enacted in the wake of World War II through the construction of Western institutions like the United Nations and the North Atlantic Treaty Organization (NATO) has been recently battered by global networks, technological upheavals and nationalism.

In promoting President Donald Trump’s ‘America First’ platform, the White House has limited the United States’ involvement on the world stage, creating a vacuum in leadership that allows hostile actors, like Russia, to challenge long-standing institutions and power structures.

“This is something that has been fraying for a long time, and generally, the power-centers of the world have been moving away from it and [are] oblivious to the proprieties of how you maintain world order. You see the results: Shambles of international diplomacy,” Charles Hill, Yale University’s diplomat-in-residence and former advisor to Henry Kissinger, told Observer. “This is causing China, Russia and Iran to redefine themselves in ways that are not compatible with the international state system… Each of them, in their own way, are able to play the system, either for it or against it as it may suit them in that particular instance.”

“What Putin seems to have been doing now, for quite some time now, is surveying the horizon and picking something to do that will be anywhere between annoying and unacceptable. And pretty much getting away with it,” added Hill. “We’ve got to inflict some kind of pain in order to get him to stop.”

Hill explained that May’s announcement on Wednesday ends Britain’s high-level contact with Russia, while also limiting the Kremlin’s radio frequency in the United Kingdom. The expulsion of Russian diplomats and the implementation of British sanctions also means that Putin will have to initiate negotiations on his own.

But the Russian president’s expected course is further antagonism.

“I imagine the Russians are likely to A) deny any involvement in the most recent episode. And B) retaliate by expelling perhaps an equivalent number of British diplomats from Moscow,” said Brands. “The realization that many Western governments are increasingly coming to is that Putin’s government is not a normal regime: It does not behave by the same set of standards we behave by.”

“There’s certainly more of a willingness these days to apply counter-pressure in hopes of having a deterrent effect,” concluded the professor.